People rely on disposable absorbent articles to help participate in, and enjoy, their daily activities.
Disposable absorbent articles, such as adult incontinence articles and diapers, are generally manufactured by combining several components. These components typically include a liquid-permeable topsheet; a liquid-impermeable backsheet attached to the topsheet; and an absorbent core located between the topsheet and the backsheet. When the disposable article is worn, the liquid-permeable topsheet is positioned next to the body of the wearer. The topsheet allows passage of bodily fluids into the absorbent core. The liquid-impermeable backsheet helps prevent leakage of fluids held in the absorbent core. The absorbent core is designed to have desirable physical properties, e.g. a high absorbent capacity and high absorption rate, so that bodily fluids can be transported from the skin of the wearer into the disposable absorbent article.
Some disposable absorbent articles are constructed with various types of elasticized waistbands and elasticized leg bands or leg cuffs. One method of constructing elasticized regions is to incorporate elastic strands into the disposable absorbent product. For example, elastic strands have been laminated between layers of polymer film and/or layers of woven or nonwoven fabrics to provide such regions. Folded-over layers have also been employed to enclose or envelop selected strands of material. These folded-over layers have been employed to enclose elastomeric strands within the waistband, leg cuff and inner barrier cuff components of disposable diapers and other disposable absorbent articles. The polymeric film or films, layers of woven or nonwoven fabrics, and/or folded-over layers may be an integral portion of the topsheet and/or backsheet discussed above, or may be separate components that are attached to the topsheet and/or backsheet.
In order to introduce an elastic strand to the product being made, a spool of the strand is generally placed on an unwind stand. The strand is then continuously unwound, in the machine direction, with the strand being attached to a substrate, such as a base layer of material, to provide a substrate composite. As stated above, examples of a base material include, but are not limited to, polymeric films and/or woven or nonwoven fabrics. If the elastic strand does not have the integrity to withstand forces placed on it during production of the article being made, then the strand may break. For example, the tension placed on a segment of the elastic strand between an unwind stand and the point of attachment on a base material may exceed the tensile strength of that segment, causing a break. Such breaks lead to costly downtime. Accordingly, producers of disposable absorbent articles, as well as other manufacturers using elastic strand as raw material in a production process, seek ways of ensuring that the strength characteristics of the elastic strand are sufficient to withstand forces placed on the strand during production, thereby decreasing or minimizing the number of breaks. Furthermore, producers of articles, such as disposable absorbent articles, seek ways of improving the function of the elastic strand in the article. Typically, one function is to help define elasticized regions so that the disposable absorbent article better fits the wearer of the article. One way of decreasing the number of strand breaks on a production machine, improving the function of elastic strand in an article, or both, is to increase certain strength characteristics of elastic strand.
Accordingly, what is needed is a method for treating an elastic strand to improve the strength of the strand; and substrate composites or disposable absorbent articles comprising such strand.
We have determined that strength characteristics of elastic strand improve when the strand is heated. Thus, the present invention is directed to improving strength characteristics of an elastic strand by heating the strand. The strand may be heated by thermal conduction and/or convection, or by irradiative methods, incorporating, for example, infrared radiation or microwave radiation, or some combination of these. If the elastic strand is made at a location different from the location where the strand is used as a raw material, the strand may be heated at either location, or both locations. Furthermore, the strand may be heated in-line, i.e. as part of the process that makes the strand or the process that uses the strand as a raw material, or off-line, i.e. in a step separate from either of the aforementioned processes. And, as noted below, the strand may be heat treated and its exposure to water or water vapor may be regulated.
One method having features of the present invention includes the steps of: providing an elastic strand, the elastic strand having been made by steps comprising extruding, spinning, or otherwise making the strand; and heating the strand so that the peak-load value of the heated elastic strand is about 10% greater, specifically about 20% greater, particularly about 30% greater, and more particularly about 40% greater than the peak-load value of the elastic strand before heating.
In some representative embodiments, the elastic strand comprises polyester, polyurethane, polyether, polyamide, polyacrylate, polyester-b-polyurethane block co-polymer, polyether-b-polyurethane block co-polymer, or polyether-b-polyamide block co-polymer.
Methods by which the elastic strand may be heated include use of infrared radiation, microwave radiation, convective heat, conductive heat, or some combination thereof.
Some methods having features of the present invention include the steps of: providing an elastic strand, the elastic strand having been made by steps comprising extruding, spinning, or otherwise making the strand; and directing the strand to an environment having a temperature of about 120xc2x0 F. or more, the strand remaining in the environment for about 4 or more hours, particularly about 8 or more hours, and more particularly about 24 or more hours.
Other methods having features of the present invention include the steps of: providing an elastic strand, the elastic strand having been made by steps comprising extruding, spinning, or otherwise making the strand; and directing the strand to an environment having a temperature of about 212xc2x0 F. or more, the strand remaining in the environment for about 2 or more hours, particularly about 4 or more hours, and more particularly about 8 or more hours.
Still other methods having features of the present invention include the steps of: providing an elastic strand, the elastic strand having been made by steps comprising extruding, spinning, or otherwise making the strand; and directing the strand to an environment having a temperature of about 150xc2x0 C. or more, the strand remaining in the environment for about 10 or more minutes, particularly about 20 or more minutes, and more particularly about 30 or more minutes.
In some representative embodiments, the strand is heated in-line on a production machine used to make a substrate composite comprising the strand or a disposable absorbent article comprising the strand.
In other embodiments of the present invention, the elastic strand is processed by steps comprising: providing an elastic strand, the elastic strand having been made by steps comprising extruding, spinning, or otherwise making the strand; heating the strand so that the peak-load value of the heated elastic strand is about 10% greater, specifically about 20% greater, particularly about 30% greater, and more particularly about 40% greater than the peak-load value of the elastic strand before heating; and regulating exposure of the strand to water or water vapor, as disclosed in co-pending U.S. Patent Application No. 60/166348, entitled xe2x80x9cMethod for Regulating Strength Degradation in an Elastic Strand,xe2x80x9d which was filed on Nov. 19, 1999 and from which the present non-provisional application both claims priority and incorporates by reference in a manner consistent herewith. The co-pending application is generally directed to a method for regulating exposure of an elastic strand to water or water vapor, thereby regulating degradation of strength characteristics of the strand due to the action of water vapor or water on the strand. Accordingly, the present invention is directed to methods encompassing both heat treating the elastic strand to increase its strength characteristics, and regulating exposure of the strand to water or water vapor to minimize or eliminate strength degradation.
Examples of various methods for regulating elastic strand""s exposure to water or water vapor which may be used before, during, or after heating of elastic strand given below.
In some embodiments, elastic strand""s exposure to water vapor is regulated before, during, or after heating such that the specific humidity around the strand does not exceed about 0.01 pounds-mass of water vapor per pound-mass of dry air, specifically about 0.05 pounds-mass of water vapor per pound-mass of dry air during: production of the strand, storage of the strand at the geographic site where the elastic strand is made, shipping of the strand between the geographic site where the elastic strand is made and the geographic site where the elastic strand is to be used as a raw material, storage of the elastic strand at the geographic site where the elastic strand is to be used as a raw material, use of the elastic strand as a raw material, or some combination thereof. In one aspect, the elastic strand is used as a raw material to produce a substrate composite comprising the elastic strand or an absorbent article comprising the elastic strand.
In another aspect, the elastic strand""s exposure to water vapor is regulated during shipping of the strand between the geographic site where the elastic strand is made and the geographic site where the elastic strand is used as a raw material.
In some representative embodiments, regulating the strand""s exposure to water vapor comprises controlling the temperature around the strand or around a container that contains the strand. For example, the temperature may be controlled to a value not exceeding about 55 degrees Fahrenheit. By regulating temperature, the maximum humidity that may be attained is regulated (i.e., as air temperature decreases, the capacity of the air to hold water vapor decreases).
In other versions of the invention, wherein regulating the strand""s exposure to water vapor comprises controlling the humidity around the strand or around a container that contains the strand.
In other versions of the invention, regulating the elastic strand""s exposure to water vapor before or after heating of the strand comprises placing the strand in a container comprising a barrier material and closing the container.
In another aspect, the container comprising a barrier material is closed at a time t1, time t1 being after the time when the strand is first produced and before the time when the strand is shipped from the geographical site at which the strand is first produced to the geographical site at which the strand is used.
In still another aspect, the specific humidity around the strand does not exceed about 0.017 pounds-mass of water vapor per pound-mass of dry air, particularly about 0.01 pounds-mass of water vapor per pound-mass of dry air, and specifically about 0.005 pounds-mass of water vapor per pound-mass of dry air, between time t1 and time t2, time t2 being the time when the closed container comprising a barrier material is first opened.
In some versions of the invention the barrier material comprises polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyester, polycarbonate, nylon, cellulose, or a combination thereof.
In another aspect, closing the container comprising a barrier material comprises heat sealing the container, the barrier material, or both.
Some representative embodiments involve placing desiccant material with the strand before heat sealing the container, the barrier material, or both. Possible desiccant materials comprise calcium chloride, calcium sulfate, silica gel, a molecular sieve, Al2O3, or some combination of thereof.
In other versions of the invention, any mixture of air and water vapor inside the container comprising a barrier material is displaced with an inert dry gas before heat sealing the container, the barrier material, or both; placing a humidity indicator inside the container comprising a barrier material before heat sealing the container, the barrier material, or both; or both of these steps.
The invention encompasses elastic strand that is heated to increase strength, as well as substrate composites and/or disposable absorbent products comprising said strand. Furthermore, as mentioned above, the elastic strand may also be handled such that the strand""s exposure to water or water vapor is regulated before, during, or after heat treatment of the strand.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.